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Redberry is an open source computer algebra system designed for tensor manipulation. It implements basic computer algebra system routines as well as complex tools for real computations in physics. This module contains the implementation of special routines needed in real physical problems. It contains tools for such problems like Feynman graphs and one-loop counterterms calculation etc.

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/*
 * Redberry: symbolic tensor computations.
 *
 * Copyright (c) 2010-2014:
 *   Stanislav Poslavsky   
 *   Bolotin Dmitriy       
 *
 * This file is part of Redberry.
 *
 * Redberry is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Redberry is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Redberry. If not, see .
 */

package cc.redberry.physics.oneloopdiv;

import cc.redberry.core.indices.IndicesUtils;
import cc.redberry.core.tensor.*;
import cc.redberry.core.transformations.Transformation;
import cc.redberry.core.utils.*;
import java.util.Arrays;

/**
 *
 * @author Dmitry Bolotin
 * @author Stanislav Poslavsky
 */
final class SqrSubs implements Transformation {

    private int name;

    public SqrSubs(SimpleTensor st) {
        if (st.getIndices().size() != 1)
            throw new IllegalArgumentException();
        name = st.getName();
    }

    @Override
    public Tensor transform(Tensor tensor) {
        if (!(tensor instanceof Product))
            return tensor;
        Product product = (Product) tensor;

        ProductContent content = product.getContent();
        StructureOfContractionsHashed cs = content.getStructureOfContractionsHashed();
        short si = content.getStretchIndexByHash(name);
        if (si == -1)
            return tensor;

        TensorContraction contraction = new TensorContraction(si, new long[]{((long) si) << 16});
        short[] sIndices = content.getStretchIds(); //For preformance.
        int index = Arrays.binarySearch(sIndices, si);
        while (index >= 0 && sIndices[index--] == si);
        ++index;
        IntArrayList list = new IntArrayList();
        do {
            Tensor t = content.get(index);
            if (!(t instanceof SimpleTensor))
                continue;
            SimpleTensor st = (SimpleTensor) t;
            if (st.getName() != name)
                continue;
            int indexName;
            if (cs.get(index).equals(contraction)
                    && ((indexName = st.getIndices().get(0)) & 0x80000000) == 0)
                list.add(indexName);
        } while (index < sIndices.length - 1 && sIndices[++index] == si);
        int[] indices = list.toArray();

        if (indices.length == 0)
            return tensor;

        Arrays.sort(indices);
        IntArrayList toRemvoe = new IntArrayList();
        Tensor current;
        int size = content.size();
        for (index = 0; index < size; ++index) {
            current = content.get(index);
            if (!(current instanceof SimpleTensor))
                continue;
            SimpleTensor st = (SimpleTensor) current;
            if (st.getName() != name)
                continue;
            if (Arrays.binarySearch(indices, IndicesUtils.getNameWithType(st.getIndices().get(0))) >= 0)
                toRemvoe.add(index);
        }
        if (toRemvoe.size() == 0)
            return tensor;

        Tensor indexless = product.getIndexlessSubProduct();
        ProductBuilder pb = new ProductBuilder();
        pb.put(indexless);

        for (int i = size - 1; i >= 0; --i)
            if (ArraysUtils.binarySearch(toRemvoe, i) < 0)//toRemove is sorted                
                pb.put(content.get(i));
        return pb.build();
    }
}